The present invention is directed to the surface modification of solid polymeric substrates and more particularly to controlled surface fluorination thereof.
Synthetic polymers and plastics provide the basis for a large part of consumer and industrial products encountered presently and likely will increase in the future. Polymeric solids, for present purposes, comprehends an object constructed from, coated with, or otherwise composed of a polymer in solid form. Examples of such polymeric solids include, for example, synthetic fibers for clothing, polyvinyl chloride (PVC) and like plastic storage bags (eg. blood bags), polycarbonate safety glasses, to name but just a few of such items. Such polymeric solids are chosen for an intended use because of particular bulk properties which they possess. That is, particular polymeric solids possess good tensile strength, desirable oxygen permeability capabilities, high impact resistance, resistance to corrosion, good optical properties, and a variety of other properties. While the bulk properties of such polymeric solids may be quite good, the outer surface of such polymeric solids often can be degraded or eroded by a variety of conditions encountered in every-day use. That is, some polymeric solids while providing good tensile strength, may become easily soiled and scratched, while other polymeric solids of good optical transmissivity can become easily soiled and are resistant to cleaning. Other polymeric solids may be subject to the phenomena known as plasticizer migration. It will be seen that the polymeric solids require a surface treatment in order to materially enhance their durability in every-day use.
One such surface treatment proposed in the art comprises subjecting the polymeric solid to a fluorine-containing source in order to surface-fluorinate the polymeric solid. For example, U.S. Pat. No. 4,296,151 proposes to treat normally solid polymers of aliphatic mono-1-olefins and elastomeric and resinous polymers of conjugated dienes and vinyl-substituted aromatic compounds with fluorine gas in order to render the surface water-wettable and resistant to hydrocarbons, thus improving the printability of the treated solid. U.S. Pat. No. 4,264,750 discloses the use of cold plasma fluorination techniques to completely fluorinate a hydrocarbon or amide polymer. Such cold plasma process is conducted with various fluorine-containing gases in the substantial absence of oxygen. U.S. Pat. No. 4,120,032 proposes an improved barrier coating polymeric film by treating such film with combination of fluorine and bromine. U.S. Pat. No. 4,076,916 conducts the fluorination of polymers by contacting the polymer initially with dilute fluorine gas (eg. 6%) followed by the gradual increase in fluorine concentration. U.S. Pat. Nos. 3,758,450 and 3,775,489 disclose surface fluorination processes utilizing such fluorination process. U.S. Pat. No. 4,020,223 proposes to fluorinate polyolefin and polyacrylonitrile fiber form by treating such fiber form with elemental fluorine in the presence of low amounts of oxygen.
While control of the fluorination reaction is an object within each of these prior art proposals, none of such proposals recognizes any universality in the surface fluorination process for virtually all types of polymeric solids. Moreover, no apparent predictability in the fluorination processes of the prior art is readily apparent. The present invention, however, provides an analysis of the chemical reactions occurring at the surface of the polymeric solids during the fluorination process and provides limitations thereon for achieving improved surface properties of the solid while substantially maintaining the bulk physical properties of the polymeric solid itself.